Pluto News, The Kuipers and Beyondhttp://www.spacedaily.com/outerplanets.html
Pluto News, The Kuipers and BeyondTue, 06 DEC 2016 02:47:14 AESTTue, 06 DEC 2016 02:47:14 AESTen-us
College Park MD (SPX) Nov 30, 2016 -
Pluto's "icy heart" is a bright, two-lobed feature on its surface that has attracted researchers ever since its discovery by the NASA New Horizons team in 2015. Of particular interest is the heart's western lobe, informally named Sputnik Planitia, a deep basin containing three kinds of ices - frozen nitrogen, methane and carbon monoxide - and appearing opposite Charon, Pluto's tidally locked moon.

Sputnik Planitia's unique attributes have spurred a number of scenarios for its formation, all of which identify the feature as an impact basin, a depression created by a smaller body striking Pluto at extremely high speed.

A new study led by Douglas Hamilton, professor of astronomy at the University of Maryland, instead suggests that Sputnik Planitia formed early in Pluto's history and that its attributes are inevitable consequences of evolutionary processes. The study was published in the journal Nature on December 1, 2016.

"The main difference between my model and others is that I suggest that the ice cap formed early, when Pluto was still spinning quickly, and that the basin formed later and not from an impact," said Hamilton, who is lead author of the paper.

"The ice cap provides a slight asymmetry that either locks toward or away from Charon when Pluto's spin slows to match the orbital motion of the moon."

Using a model he developed, Hamilton found that the initial location of Sputnik Planitia could be explained by Pluto's unusual climate and its spin axis, which is tilted by 120 degrees.

For comparison, Earth's tilt is 23.5 degrees. Modeling the dwarf planet's temperatures showed that when averaged over Pluto's 248-year orbit, the 30 degrees north and south latitudes emerged as the coldest places on the dwarf planet, far colder than either pole. Ice would have naturally formed around these latitudes, including at the center of Sputnik Planitia, which is located at 25 degrees north latitude.

Hamilton's model also showed that a small ice deposit naturally attracts more ices by reflecting away solar light and heat. Temperatures remain low, which attracts more ice and keeps the temperature low, and the cycle repeats.

This positive feedback phenomenon, called the runaway albedo effect, would eventually lead to a single dominating ice cap, like the one observed on Pluto. However, Pluto's basin is significantly larger than the volume of ice it contains today, suggesting that Pluto's heart has been slowly losing mass over time, almost as if it was wasting away.

Even so, the single ice cap represents an enormous weight on Pluto's surface, enough to shift the dwarf planet's center of mass. Pluto's rotation slowed gradually due to gravitational forces from Charon, just as Earth is slowly losing spin under similar forces from its moon.

However, because Charon is so large and so close to Pluto, the process led to Pluto locking one face toward its moon in just a few million years. The large mass of Sputnik Planitia would have had a 50 percent chance of either facing Charon directly or turning as far away from the moon as possible.

"It is like a Vegas slot machine with just two states, and Sputnik Planitia ended up in the latter position, centered at 175 degrees longitude," said Hamilton.

It would also be easy for the accumulated ice to create its own basin, simply by pushing down, according to Hamilton.

"Pluto's big heart weighs heavily on the small planet, leading inevitably to depression," said Hamilton, noting that the same phenomenon happens on Earth: the Greenland Ice Sheet created a basin and pushed down the crust that it rests upon.

While Hamilton's model can explain both the latitude and longitude of Sputnik Planitia, as well as the fact that the ices exist in a basin, several other models were also presented in the December 1, 2016, issue of the journal Nature.

In one of those papers, UC Santa Cruz Professor of Earth and Planetary Sciences Francis Nimmo, Hamilton and their co-authors modeled how Sputnik Planitia may have formed if its basin was caused by an impact, such as the one that created Charon. Their results showed that the basin may have formed after Pluto slowed its rotation, migrating only slightly to its present location. If this late formation scenario proves correct, the properties of Sputnik Planitia may hint at the presence of a subsurface ocean on Pluto.

"Either model is viable under the right conditions," said Hamilton. "While we cannot conclude definitively that there is an ocean under Pluto's icy shell, we also cannot state that there is not one."

Although Pluto was stripped of its status as a planet, an ice cap is a surprisingly Earth-like property. In fact, Pluto is only the third body - Earth and Mars being the others - known to possess an ice cap. The ices of Sputnik Planitia may therefore offer hints relevant to more familiar ices here on Earth.

Tue, 06 DEC 2016 02:47:14 AEST
Tucson AZ (SPX) Nov 17, 2016 -
Sputnik Planitia, a 1,000-kilometer wide basin within the iconic heart-shaped region observed on Pluto's surface, could be in its present location because accumulation of ice made the dwarf planet roll over, creating cracks and tensions in the crust that point towards the presence of a subsurface ocean.

Published in the Nov. 17 issue of Nature, these are the conclusions of research by James Keane, a doctoral student at the University of Arizona's Lunar and Planetary Laboratory, and his adviser, assistant professor Isamu Matsuyama. They propose evidence of frozen nitrogen pileup throwing the entire planet off kilter, much like a spinning top with a wad of gum stuck to it, in a process called true polar wander.

"There are two ways to change the spin of a planet," Keane said. "The first - and the one we're all most familiar with - is a change in the planet is a change in the planet's obliquity, where the spin axis of the planet is reorienting with respect to the rest of the solar system. The second way is through true polar wander, where the spin axis remains fixed with respect to the rest of the solar system, but the planet reorients beneath it."

Planets like to spin in such a way that minimizes energy. In short, this means that planets like to reorient to place any extra mass closer to the equator, and any mass deficits closer to the pole. For example, if a giant volcano were to grow on Los Angeles, the earth would reorient itself to place L.A. on the equator.

To understand polar wander on Pluto, one first has to realize that unlike Earth, whose spin axis is only slightly tilted so that the regions around the equator receive the most sunlight, Pluto is like a spinning top lying on its side. Therefore, the planet's poles get the most sunlight. Depending on the season, it's either one or the other, while Pluto's equatorial regions are extremely cold, all the time.

Because Pluto is almost 40 times farther from the sun than we are, it takes the little ball of rock and ice 248 Earth years to complete one of its own years. At Pluto's lower latitudes near the equator, temperatures are almost as cold as minus 400 degrees Fahrenheit, cold enough to turn nitrogen into a frozen solid.

Over the course of a Pluto year, nitrogen and other exotic gases condense on the permanently shadowed regions, and eventually, as Pluto goes around the sun, those frozen gases heat up, become gaseous again and re-condense on the other side of the planet, resulting in seasonal "snowfall" on Sputnik Planitia.

"Each time Pluto goes around the sun, a bit of nitrogen accumulates in the heart," Keane said. "And once enough ice has piled up, maybe a hundred meters thick, it starts to overwhelm the planet's shape, which dictates the planet's orientation. And if you have an excess of mass in one spot on the planet, it wants to go to the equator. Eventually, over millions of years, it will drag the whole planet over."

In a sense, Pluto is a (dwarf) planet whose shape and position in space are controlled by its weather.

"I think this idea of a whole planet being dragged around by the cycling of volatiles is not something many people had really thought about before," Keane said.

The two researchers used observations made during New Horizons' flyby and combined them with computer models that allowed them to take a surface feature such as Sputnik Planitia, shift it around on the planet's surface and see what that does to the planet's spin axis. And sure enough, in the models, the geographic location of Sputnik Planitia ended up suspiciously close to where one would expect it to be.

If Sputnik Planitia were a large positive mass anomaly - perhaps due to loading of nitrogen ice - it would naturally migrate to Pluto's tidal axis with regard to Charon, Pluto's largest moon, as it approaches a minimum energy state, according to Keane and Matsuyama. In other words, the massive accumulation of ice would end up where it causes the least wobble in Pluto's spin axis.

This phenomenon of polar wander is something that was discovered with the Earth's moon and with Mars, as well, but in those cases it happened in the distant past, billions of years ago.

"On Pluto, those processes are currently active," Keane said. "Its entire geology - glaciers, mountains, valleys - seems to be linked to volatile processes. That's different from most other planets and moons in our solar system."

And not only that, the simulations and calculations also predicted that the accumulation of frozen volatiles in Pluto's heart would cause cracks and faults in the planet's surface in the exact same locations where New Horizons saw them.

The presence of tectonic faults on Pluto hint at the existence of a subsurface ocean at some point in Pluto's history, Keane explained.

"It's like freezing ice cubes," he said. "As the water turns to ice, it expands. On a planetary scale, this process breaks the surface around the planet and creates the faults we see today."

The paper is published alongside a report by Francis Nimmo of the University of California Santa Cruz and colleagues, who also consider the implications for Pluto's apparent reorientation. The authors of that paper agree with the idea that tidal forces could explain the current location of Sputnik Planitia, but in order for their model to work, a subsurface ocean would have to be present on Pluto today.

Both publications underscore the notion of a surprisingly active Pluto.

"Before New Horizons, people usually only thought of volatiles in terms of a thin frost veneer, a surface effect that might change the color, or affect local or regional geology," Keane said. "That the movement of volatiles and shifting ice around a planet could have a dramatic, planet-moving effect is not something anyone would have predicted."

Tue, 06 DEC 2016 02:47:14 AEST
Santa Cruz CA (SPX) Nov 17, 2016 -
A liquid ocean lying deep beneath Pluto's frozen surface is the best explanation for features revealed by NASA's New Horizons spacecraft, according to a new analysis. The idea that Pluto has a subsurface ocean is not new, but the study provides the most detailed investigation yet of its likely role in the evolution of key features such as the vast, low-lying plain known as Sputnik Planitia (formerly Sputnik Planum).

Sputnik Planitia, which forms one side of the famous heart-shaped feature seen in the first New Horizons images, is suspiciously well aligned with Pluto's tidal axis. The likelihood that this is just a coincidence is only 5 percent, so the alignment suggests that extra mass in that location interacted with tidal forces between Pluto and its moon Charon to reorient Pluto, putting Sputnik Planitia directly opposite the side facing Charon. But a deep basin seems unlikely to provide the extra mass needed to cause that kind of reorientation.

"It's a big, elliptical hole in the ground, so the extra weight must be hiding somewhere beneath the surface. And an ocean is a natural way to get that," said Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz and first author of a paper on the new findings published November 16 in Nature. Another paper in the same issue, led by James Keane at the University of Arizona, also argues for reorientation and points to fractures on Pluto as evidence that this happened.

Like other large basins in the solar system, Sputnik Planitia was most likely created by the impact of a giant meteorite, which would have blasted away a huge amount of Pluto's icy crust. With a subsurface ocean, the response to this would be an upwelling of water pushing up against the thinned and weakened crust of ice. At equilibrium, because water is denser than ice, that would still leave a fairly deep basin with a thin crust of ice over the upwelled mass of water.

"At that point, there is no extra mass at Sputnik Planitia," Nimmo explained. "What happens then is the ice shell gets cold and strong, and the basin fills with nitrogen ice. That nitrogen represents the excess mass."

Nimmo and his colleages also considered whether the extra mass could be provided by just a deep crater filled with nitrogen ice, with no upwelling of a subsurface ocean. But their calculations showed that this would require an implausibly deep layer of nitrogen, more than 25 miles (40 kilometers) thick. They found that a nitrogen layer about 4 miles (7 km) thick above a subsurface ocean provides enough mass to create a "positive gravity anomaly" consistent with the observations.

"We tried to think of other ways to get a positive gravity anomaly, and none of them look as likely as a subsurface ocean," Nimmo said.

Coauthor Douglas Hamilton of the University of Maryland came up with the reorientation hypothesis, and Nimmo developed the subsurface ocean scenario. The scenario is analogous to what occurred on the moon, where positive gravity anomalies have been accurately measured for several large impact basins. Instead of a subsurface ocean, however, the dense mantle material beneath the moon's crust pushed up against the thinned crust of the impact basins. Lava flows then flooded the basins, adding the extra mass. On icy Pluto, the basin filled with frozen nitrogen.

"There's plenty of nitrogen in Pluto's atmosphere, and either it preferentially freezes out in this low basin, or it freezes out in the high areas surrounding the basin and flows down as glaciers," Nimmo said. The images from New Horizons do show what appear to be nitrogen glaciers flowing out of mountainous terrain around Sputnik Planitia.

As for the subsurface ocean, Nimmo said he suspects it is mostly water with some kind of antifreeze in it, probably ammonia. The slow refreezing of the ocean would put stress on the icy shell, causing fractures consistent with features seen in the New Horizons images.

There are other large objects in the Kuiper belt that are similar to Pluto in size and density, and Nimmo said they probably also have subsurface oceans. "When we look at these other objects, they may be equally interesting, not just frozen snowballs," he said.

Tue, 06 DEC 2016 02:47:14 AEST
Santa Cruz CA (SPX) Nov 16, 2016 -
A liquid ocean lying deep beneath Pluto's frozen surface is the best explanation for features revealed by NASA's New Horizons spacecraft, according to a new analysis. The idea that Pluto has a subsurface ocean is not new, but the study provides the most detailed investigation yet of its likely role in the evolution of key features such as the vast, low-lying plain known as Sputnik Planitia (formerly Sputnik Planum).

Sputnik Planitia, which forms one side of the famous heart-shaped feature seen in the first New Horizons images, is suspiciously well aligned with Pluto's tidal axis. The likelihood that this is just a coincidence is only 5 percent, so the alignment suggests that extra mass in that location interacted with tidal forces between Pluto and its moon Charon to reorient Pluto, putting Sputnik Planitia directly opposite the side facing Charon. But a deep basin seems unlikely to provide the extra mass needed to cause that kind of reorientation.

"It's a big, elliptical hole in the ground, so the extra weight must be hiding somewhere beneath the surface. And an ocean is a natural way to get that," said Francis Nimmo, professor of Earth and planetary sciences at UC Santa Cruz and first author of a paper on the new findings published in Nature [http://www.nature.com].

Another paper in the same issue, led by James Keane at the University of Arizona, also argues for reorientation and points to fractures on Pluto as evidence that this happened.

Like other large basins in the solar system, Sputnik Planitia was most likely created by the impact of a giant meteorite, which would have blasted away a huge amount of Pluto's icy crust. With a subsurface ocean, the response to this would be an upwelling of water pushing up against the thinned and weakened crust of ice. At equilibrium, because water is denser than ice, that would still leave a fairly deep basin with a thin crust of ice over the upwelled mass of water.

"At that point, there is no extra mass at Sputnik Planitia," Nimmo explained. "What happens then is the ice shell gets cold and strong, and the basin fills with nitrogen ice. That nitrogen represents the excess mass."

Nimmo and his colleagues also considered whether the extra mass could be provided by just a deep crater filled with nitrogen ice, with no upwelling of a subsurface ocean. But their calculations showed that this would require an implausibly deep layer of nitrogen, more than 25 miles (40 kilometers) thick. They found that a nitrogen layer about 4 miles (7 km) thick above a subsurface ocean provides enough mass to create a "positive gravity anomaly" consistent with the observations.

"We tried to think of other ways to get a positive gravity anomaly, and none of them look as likely as a subsurface ocean," Nimmo said.

Coauthor Douglas Hamilton of the University of Maryland came up with the reorientation hypothesis, and Nimmo developed the subsurface ocean scenario. The scenario is analogous to what occurred on the Moon, where positive gravity anomalies have been accurately measured for several large impact basins. Instead of a subsurface ocean, however, the dense mantle material beneath the Moon's crust pushed up against the thinned crust of the impact basins. Lava flows then flooded the basins, adding the extra mass. On icy Pluto, the basin filled with frozen nitrogen.

"There's plenty of nitrogen in Pluto's atmosphere, and either it preferentially freezes out in this low basin, or it freezes out in the high areas surrounding the basin and flows down as glaciers," Nimmo said. The images from New Horizons do show what appear to be nitrogen glaciers flowing out of mountainous terrain around Sputnik Planitia.

As for the subsurface ocean, Nimmo said he suspects it is mostly water with some kind of antifreeze in it, probably ammonia. The slow refreezing of the ocean would put stress on the icy shell, causing fractures consistent with features seen in the New Horizons images.

There are other large objects in the Kuiper belt that are similar to Pluto in size and density, and Nimmo said they probably also have subsurface oceans. "When we look at these other objects, they may be equally interesting, not just frozen snowballs," he said.

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Tue, 06 DEC 2016 02:47:14 AEST
Kobe, Japan (SPX) Nov 02, 2016 -
A team of researchers has presented a new model for the origin of Saturn's rings based on results of computer simulations. The results of the simulations are also applicable to rings of other giant planets and explain the compositional differences between the rings of Saturn and Uranus. The findings were published on October 6 in the online version of Icarus.

The giant planets in our solar system have very diverse rings. Observations show that Saturn's rings are made of more than 95% icy particles, while the rings of Uranus and Neptune are darker and may have higher rock content. Since the rings of Saturn were first observed in the 17th century, investigation of the rings has expanded from earth-based telescopes to spacecraft such as Voyagers and Cassini.

However, the origin of the rings was still unclear and the mechanisms that lead to the diverse ring systems were unknown.

The present study focused on the period called the Late Heavy Bombardment that is believed to have occurred 4 billion years ago in our solar system, when the giant planets underwent orbital migration. It is thought that several thousand Pluto-sized (one fifth of Earth's size) objects from the Kuiper belt existed in the outer solar system beyond Neptune.

First the researchers calculated the probability that these large objects passed close enough to the giant planets to be destroyed by their tidal force during the Late Heavy Bombardment. Results showed that Saturn, Uranus and Neptune experienced close encounters with these large celestial objects multiple times.

Next the group used computer simulations to investigate disruption of these Kuiper belt objects by tidal force when they passed the vicinity of the giant planets (see Figure 2a). The results of the simulations varied depending on the initial conditions, such as the rotation of the passing objects and their minimum approach distance to the planet.

However they discovered that in many cases fragments comprising 0.1-10% of the initial mass of the passing objects were captured into orbits around the planet (see Figures 2a, b). The combined mass of these captured fragments was found to be sufficient to explain the mass of the current rings around Saturn and Uranus. In other words, these planetary rings were formed when sufficiently large objects passed very close to giants and were destroyed.

The researchers also simulated the long-term evolution of the captured fragments using supercomputers at the National Astronomical Observatory of Japan. From these simulations they found that captured fragments with an initial size of several kilometers are expected to undergo high-speed collisions repeatedly and are gradually shattered into small pieces. Such collisions between fragments are also expected to circularize their orbits and lead to the formation of the rings observed today (see Figures 2b, c).

This model can also explain the compositional difference between the rings of Saturn and Uranus. Compared to Saturn, Uranus (and also Neptune) has higher density (the mean density of Uranus is 1.27g cm-3, and 1.64g cm-3 for Neptune, while that of Saturn is 0.69g cm-3).

This means that in the cases of Uranus (and Neptune), objects can pass within close vicinity of the planet, where they experience extremely strong tidal forces. (Saturn has a lower density and a large diameter-to-mass ratio, so if objects pass very close they will collide with the planet itself).

As a result, if Kuiper belt objects have layered structures such as a rocky core with an icy mantle and pass within close vicinity of Uranus or Neptune, in addition to the icy mantle, even the rocky core will be destroyed and captured, forming rings that include rocky composition. However if they pass by Saturn, only the icy mantle will be destroyed, forming icy rings. This explains the different ring compositions.

These findings illustrate that the rings of giant planets are natural by-products of the formation process of the planets in our solar system. This implies that giant planets discovered around other stars likely have rings formed by a similar process. Discovery of a ring system around an exoplanet has been recently reported, and further discoveries of rings and satellites around exoplanets will advance our understanding of their origin.

Tue, 06 DEC 2016 02:47:14 AEST
Laurel MD (SPX) Oct 28, 2016 -
NASA's New Horizons mission reached a major milestone this week when the last bits of science data from the Pluto flyby - stored on the spacecraft's digital recorders since July 2015 - arrived safely on Earth.

Having traveled from the New Horizons spacecraft over 3.1 billion miles (five hours, eight minutes at light speed), the final item - a segment of a Pluto-Charon observation sequence taken by the Ralph/LEISA imager - arrived at mission operations at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, at 5:48 a.m. EDT on Oct. 25.

The downlink came via NASA's Deep Space Network station in Canberra, Australia. It was the last of the 50-plus total gigabits of Pluto system data transmitted to Earth by New Horizons over the past 15 months.

"The Pluto system data that New Horizons collected has amazed us over and over again with the beauty and complexity of Pluto and its system of moons," said Alan Stern, New Horizons principal investigator from Southwest Research Institute in Boulder, Colorado.

"There's a great deal of work ahead for us to understand the 400-plus scientific observations that have all been sent to Earth. And that's exactly what we're going to do - after all, who knows when the next data from a spacecraft visiting Pluto will be sent?"

Because it had only one shot at its target, New Horizons was designed to gather as much data as it could, as quickly as it could - taking about 100 times more data on close approach to Pluto and its moons than it could have sent home before flying onward.

The spacecraft was programmed to send select, high-priority datasets home in the days just before and after close approach, and began returning the vast amount of remaining stored data in September 2015.

Bowman said the team will conduct a final data-verification review before erasing the two onboard recorders, and clearing space for new data to be taken during the New Horizons Kuiper Belt Extended Mission (KEM) that will include a series of distant Kuiper Belt object observations and a close encounter with a small Kuiper Belt object, 2014 MU69, on Jan. 1, 2019.

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Tue, 06 DEC 2016 02:47:14 AEST
Pasadena CA (JPL) Oct 25, 2016 -
NASA's Voyager 2 spacecraft flew by Uranus 30 years ago, but researchers are still making discoveries from the data it gathered then. A new study led by University of Idaho researchers suggests there could be two tiny, previously undiscovered moonlets orbiting near two of the planet's rings.

Rob Chancia, a University of Idaho doctoral student, spotted key patterns in the rings while examining decades-old images of Uranus' icy rings taken by Voyager 2 in 1986. He noticed the amount of ring material on the edge of the alpha ring - one of the brightest of Uranus' multiple rings - varied periodically. A similar, even more promising pattern occurred in the same part of the neighboring beta ring.

"When you look at this pattern in different places around the ring, the wavelength is different - that points to something changing as you go around the ring. There's something breaking the symmetry," said Matt Hedman, an assistant professor of physics at the University of Idaho, who worked with Chancia to investigate the finding.

Their results will be published in The Astronomical Journal and have been posted to the pre-press site arXiv.

Chancia and Hedman are well-versed in the physics of planetary rings: both study Saturn's rings using data from NASA's Cassini spacecraft, which is currently orbiting Saturn. Data from Cassini have yielded new ideas about how rings behave, and a grant from NASA allowed Chancia and Hedman to examine Uranus data gathered by Voyager 2 in a new light.

Specifically, they analyzed radio occultations - made when Voyager 2 sent radio waves through the rings to be detected back on Earth - and stellar occultations, made when the spacecraft measured the light of background stars shining through the rings, which helps reveal how much material they contain.

They found the pattern in Uranus' rings was similar to moon-related structures in Saturn's rings called moonlet wakes.

The researchers estimate the hypothesized moonlets in Uranus' rings would be 2 to 9 miles (4 to 14 kilometers) in diameter - as small as some identified moons of Saturn, but smaller than any of Uranus' known moons. Uranian moons are especially hard to spot because their surfaces are covered in dark material.

"We haven't seen the moons yet, but the idea is the size of the moons needed to make these features is quite small, and they could have easily been missed," Hedman said. "The Voyager images weren't sensitive enough to easily see these moons."

Hedman said their findings could help explain some characteristics of Uranus' rings, which are strangely narrow compared to Saturn's. The moonlets, if they exist, may be acting as "shepherd" moons, helping to keep the rings from spreading out. Two of Uranus' 27 known moons, Ophelia and Cordelia, act as shepherds to Uranus' epsilon ring.

"The problem of keeping rings narrow has been around since the discovery of the Uranian ring system in 1977 and has been worked on by many dynamicists over the years," Chancia said. "I would be very pleased if these proposed moonlets turn out to be real and we can use them to approach a solution."

Confirming whether or not the moonlets actually exist using telescope or spacecraft images will be left to other researchers, Chancia and Hedman said. They will continue examining patterns and structures in Uranus' rings, helping uncover more of the planet's many secrets.

"It's exciting to see Voyager 2's historic Uranus exploration still contributing new knowledge about the planets," said Ed Stone, project scientist for Voyager, based at Caltech, Pasadena, California.

Voyager 2 and its twin, Voyager 1, were launched 16 days apart in 1977. Both spacecraft flew by Jupiter and Saturn, and Voyager 2 also flew by Uranus and Neptune. Voyager 2 is the longest continuously operated spacecraft.

It is expected to enter interstellar space in a few years, joining Voyager 1, which crossed over in 2012. Though far past the planets, the mission continues to send back unprecedented observations of the space environment in the solar system, providing crucial information on the environment our spacecraft travel through as we explore farther and farther from home.

Tue, 06 DEC 2016 02:47:14 AEST
Pasadena CA (JPL) Oct 19, 2016 -
The next target for NASA's New Horizons mission - which made a historic flight past Pluto in July 2015 - apparently bears a colorful resemblance to its famous, main destination.

NASA's Hubble Space Telescope data suggests that 2014 MU69, a small Kuiper Belt object (KBO) about a billion miles (1.6 billion kilometers) beyond Pluto, is as red, if not redder, than Pluto. This is the first hint at the surface properties of the far-flung object that New Horizons will survey on Jan. 1, 2019.

Mission scientists are discussing this and other Pluto and Kuiper Belt findings this week at the American Astronomical Society Division for Planetary Sciences (DPS) and European Planetary Science Congress (EPSC) meeting in Pasadena, California.

"We're excited about the exploration ahead for New Horizons, and also about what we are still discovering from Pluto flyby data," said Alan Stern, principal investigator from Southwest Research Institute in Boulder, Colorado. "Now, with our spacecraft transmitting the last of its data from last summer's flight through the Pluto system, we know that the next great exploration of Pluto will require another mission to be sent there."

Stern said that Pluto's complex, layered atmosphere is hazy and appears to be mostly free of clouds, but the team has spied a handful of potential clouds in images taken with New Horizons' cameras. "If there are clouds, it would mean the weather on Pluto is even more complex than we imagined," Stern said.

Scientists already knew from telescope observations that Pluto's icy surface below that atmosphere varied widely in brightness. Data from the flyby not only confirms that, it also shows the brightest areas (such as sections of Pluto's large heart-shaped region) are among the most reflective in the solar system. "That brightness indicates surface activity," said Bonnie Buratti, a science team co-investigator from NASA's Jet Propulsion Laboratory in Pasadena.

"Because we see a pattern of high surface reflectivity equating to activity, we can infer that the dwarf planet Eris, which is known to be highly reflective, is also likely to be active."

While Pluto shows many kinds of activity, one surface process apparently missing is landslides. Surprisingly, though, they have been spotted on Pluto's largest moon, Charon, itself some 750 miles (1,200 kilometers) across.

"We've seen similar landslides on other rocky and icy planets, such as Mars and Saturn's moon Iapetus, but these are the first landslides we've seen this far from the sun, in the Kuiper Belt," said Ross Beyer, a science team researcher from Sagan Center at the SETI Institute and NASA Ames Research Center, Moffett Field, California. "The big question is will they be detected elsewhere in the Kuiper Belt?"

Both Hubble and cameras on the New Horizons spacecraft have been aimed at KBOs over the past two years, with New Horizons taking advantage of its unique vantage point in the Kuiper Belt to observe nearly a dozen small worlds in this barely explored region. MU69 is actually the smallest KBO to have its color measured - and scientists have used that data to confirm the object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the solar system.

"The reddish color tells us the type of Kuiper Belt object 2014 MU69 is," said Amanda Zangari, a New Horizons post-doctoral researcher from Southwest Research Institute. "The data confirms that on New Year's Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets."

The New Horizons spacecraft is currently 3.4 billion miles (5.5 billion kilometers) from Earth and about 340 million miles (540 million kilometers) beyond Pluto, speeding away from the sun at about nine miles (14 kilometers) every second.

About 99 percent of the data New Horizons gathered and stored on its digital recorders during the Pluto encounter has now been transmitted back to Earth, with that transmission set to be completed Oct. 23. New Horizons has covered about one-third of the distance from Pluto to its next flyby target, which is now about 600 million miles (nearly 1 billion kilometers) ahead.

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Tue, 06 DEC 2016 02:47:14 AEST
Pasadena CA (SPX) Oct 24, 2016 -
Planet Nine - the undiscovered planet at the edge of the solar system that was predicted by the work of Caltech's Konstantin Batygin and Mike Brown in January 2016 - appears to be responsible for the unusual tilt of the Sun, according to a new study. The large and distant planet may be adding a wobble to the solar system, giving the appearance that the Sun is tilted slightly.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.

All of the planets orbit in a flat plane with respect to the Sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the Sun - giving the appearance that the Sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect.

"It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

Brown and Batygin's discovery of evidence that the Sun is orbited by an as-yet-unseen planet - that is about 10 times the size of Earth with an orbit that is about 20 times farther from the Sun on average than Neptune's - changes the physics.

Planet Nine, based on their calculations, appears to orbit at about 30 degrees off from the other planets' orbital plane - in the process, influencing the orbit of a large population of objects in the Kuiper Belt, which is how Brown and Batygin came to suspect a planet existed there in the first place.

"It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery," says Batygin, an assistant professor of planetary science.

Their findings have been accepted for publication in an upcoming issue of the Astrophysical Journal, and will be presented this week at the American Astronomical Society's Division for Planetary Sciences 48th annual meeting, held jointly in Pasadena, California, with the 11th European Planetary Science Congress.

The tilt of the solar system's orbital plane has long befuddled astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star.

Planet Nine's angular momentum is having an outsized impact on the solar system based on its location and size. A planet's angular momentum equals the mass of an object multiplied by its distance from the Sun, and corresponds with the force that the planet exerts on the overall system's spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.

Planet Nine's unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.

The next question, then, is how did Planet Nine achieve its unusual orbit? Though that remains to be determined, Batygin suggests that the planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar system's extreme past.

For now, Brown and Batygin continue to work with colleagues throughout the world to search the night sky for signs of Planet Nine along the path they predicted in January. That search, Brown says, may take three years or more.

Tue, 06 DEC 2016 02:47:14 AEST
Paris, France (SPX) Sep 21, 2016 -
What is the origin of the large heart-shaped nitrogen glacier revealed in 2015 on Pluto by the New Horizons spacecraft? Two researchers from the Laboratoire de meteorologie dynamique show that Pluto's peculiar insolation and atmosphere favor nitrogen condensation near the equator, in the lower altitude regions, leading to an accumulation of ice at the bottom of Sputnik Planum, a vast topographic basin.

Through their simulations, they also explain the surface distribution and atmospheric abundance of other types of volatiles observed on Pluto. These results are published in Nature on September 19, 2016.

Pluto is a paradise for glaciologists. Among the types of ice covering its surface, nitrogen is the most volatile: when it sublimes (at -235C), it forms a thin atmosphere in equilibrium with the ice reservoir at the surface.

One of the most unexpected observations from New Horizons, which flew by Pluto in July 2015, showed that this reservoir of solid nitrogen is extremely massive, and mostly contained in "Sputnik Planum", a topographic basin located within the tropics of Pluto. Methane frost also appears all over the northern hemisphere, except at the equator, while carbon monoxide ice in smaller amounts was only detected in Sputnik Planum.

Until now, the distribution of Pluto's ice remained unexplained. To better understand the physical processes at work on Pluto, the researchers developed a numerical thermal model of the surface of the dwarf planet able to simulate the nitrogen, methane and carbon monoxide cycles over thousands of years, and compared the results with the observations made by the New Horizons spacecraft.

Their model shows that the solid-gas equilibrium of nitrogen is responsible for trapping the ice in Sputnik Planum. At the bottom of the basin, the pressure of the atmosphere - and therefore of gaseous nitrogen - increases, and the corresponding frost temperature is higher than outside the basin, which allows the nitrogen to preferably condense into ice.
Simulations show that the nitrogen ice inevitably accumulates in the basin, thus forming a permanent nitrogen reservoir, as observed by New Horizons.

The numerical simulations also describe the methane and carbon monoxide cycles. Because of its volatility similar to that of nitrogen, carbon monoxide ice is entirely sequestered with nitrogen in the basin, in keeping with the New Horizons measurements.

Regarding the methane ice, its lower volatility at the temperatures prevailing on Pluto allows it to exist elsewhere than in the Sputnik Planum glacier. The model shows that pure methane ice seasonally covers both hemispheres, in agreement with New Horizons data.

This scenario shows that there is no need for an internal reservoir of nitrogen ice to explain the formation of the Sputnik Planum glacier, as suggested by previous studies. Instead, well-known physical principles underlie this icy cocktail on Pluto and its spectacular activity, one of the most fascinating in the Solar System.

The researchers also predict that atmospheric pressure is at its seasonal peak and will decrease in the next decades, while seasonal frosts will tend to disappear.